Added interpose driver from DLS

Added a low-level interpose driver to allow usage of stream devices.

src/pmacAsynIPPort.h

@@ -0,0 +1,35 @@
+#ifndef asynInterposePmac_H
+#define asynInterposePmac_H
+
+#include <epicsExport.h>
+#include <shareLib.h>
+
+/*
+Value is chosen arbitrarily, it just needs to be unique
+*/
+#define FLUSH_HARDWARE 1
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+/**
+ * @brief Initialize a special asyn IP Port for PMAC controllers.
+ *
+ * Function that first initialises an asyn IP port and then the PMAC Asyn IP
+ * interpose layer. It is a wrapper for drvAsynIPPort::drvAsynIPPortConfigure()
+ * and pmacAsynIPPort::pmacAsynIPPortConfigureEos().
+ *
+ * @param portName The Asyn Port name string.
+ * @param hostInfo The hostname or IP address followed by IP port (eg.
+ * 172.23.243.156:1025)
+ * @return status
+ */
+epicsShareFunc int pmacAsynIPPortConfigure(const char *portName,
+                                           const char *hostInfo);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif /* asynInterposePmac_H */